It's posible to warp a head and not leak coolant into the engine oil. I've seen it before. Has the car ever been overheated? If not, I'm betting you have a cracked head... Check for hair-line cracks around where the studs go through and around the coolant passages. They will be small so look hard. As long as you have the head off, take it to a machine shop that rebuilds engines and have them look it over. They may be able to give you some help.